`_PyObject_IS_GC()` should not use `PyType_HasFeature()`

[neonene]

Feature or enhancement

Proposal:

_PyObject_IS_GC() is one of the most frequently used functions, which keeps using PyType_HasFeature() rather than _PyType_HasFeature().

I know it has no performance issues since introduced, but switching to use _PyType_HasFeature() would make more sense:

• Include/internal/pycore_object.h

// Fast inlined version of PyObject_IS_GC()
static inline int
_PyObject_IS_GC(PyObject *obj)
{
    PyTypeObject *type = Py_TYPE(obj);
    return (PyType_IS_GC(type)
            && (type->tp_is_gc == NULL || type->tp_is_gc(obj)));
}
...
// Fast inlined version of PyType_IS_GC()
#define _PyType_IS_GC(t) _PyType_HasFeature((t), Py_TPFLAGS_HAVE_GC)

• Include/objimpl.h

/* Test if a type has a GC head */
#define PyType_IS_GC(t) PyType_HasFeature((t), Py_TPFLAGS_HAVE_GC)

cc @vstinner

Linked PRs

• gh-124344: Make _PyObject_IS_GC() use underscored PyType_IS_GC() #124349

[vstinner]

Do you want to propose a PR?

[vstinner]

Implemented in d9d5b3d.